Sulfuric acid alkylation with eeffluent refrigeration and depropanizer bottoms flashing



R. SMITH ErAL 2,988,580 LATION WITH EFFLUENT REFRIGERATION `lune 13, 1961 SULFURIC ACID ALKY AND DEPROPANIZER BOTTOMS FLASHING Filed Oct. 13, 1958 w M m www E v/ V f i www M M MM r d Z 0.a P @HW um. .Q

United States Patent SULFURIC ACID ALKYLATION WITH EFFLUENT REFRIGERATION AND DEPROPANIZER BOT- TOMS FLASHING Randlow Smith, New Rochelle, and Charles W. Petterson,

New York, N.Y., assignors to Texaco Inc., a corporation of Delaware Filed Oct. 13, 1958, Ser. No. 767,058 6 Claims. (Cl. 260--683.62)

This invention relates to catalytic isobutane-olefin alkylation with a liquid catalyst, and more particularly to such an alkylation process employing effluent refrigeration.

This application is a continuation-impart of our copending patent application of the same title having Serial No. 447,153, filed on August 2, 1954 and now abandoned.

Reissue Patent No. 22,146 of No. 2,256,880, Goldsby and Van Gundy, teaches the principles of effluent refrigeration. This patent discloses isobutane-olefin catalytic alkylation, wherein the efuent from the alkylation zone is separated into a hydrocarbon phase and an acid phase, the separated hydrocarbon phase is passed to a flash zone of lower pressure where isobutane is vaporized with concomitant cooling of the remaining liquid hydrocarbons including alkylate, and the resulting cooled or chilled liquid hydrocarbons are utilized to maintain or assist in maintaining the temperature in the alkylation zone by indirect heat exchange therewith. This patent also discloses that the vaporized isobutane from the flash zone is removed and compressed for recycling to the alkylation zone.

Effluent refrigeration possesses certain advantages over autorefrigeration of the alkylation reaction zone in which lower boiling hydrocarbons including isobutane are evaporated directly from the alkylation reaction zone. In efiluent refrigeration, the alkylation zone and settler are maintained under sufficient pressure to prevent evaporation of any substantial amount of the lower boiling hydrocarbons and thereby insure keeping isobutane and other reactants in liquid phase, whereby the desired high molar excess of liquid isobutane over olefin is maintained throughout the alkylation zone.

Patent No. 2,334,955, Putney, also discloses eluent refrigeration in catalytic isobutane-olefin alkylation, and suggests that a portion of the chilled hydrocarbon liquid from the flash zone can be passed in indirect heat exchange with the feed of reactants to the alkylation zone (page l, column 2, lines 35-39). This patent teaches the principle in effluent refrigeration of dividing the refrigeration load for the alkylation step between effluent refrigeration supplied to the alkylation zone and effluent refrigeration supplied to pre-chill the feed to the alkylation zone.

Patent No. 2,664,452, Putney, teaches a further mprovement in effluent refrigeration involving a double flash drum arrangement for accomplishing this division of the refrigeration load for the alkylation zone. Thus, vaporized isobutane from the first flash zone, which supplies the chilled hydrocarbon liquid used for refrigeration of both the alkylation reaction zone and also the feed to the alkylation zone, is compressed and condensed, a portion of the condensed isobutane is passed to the alkylate fractionating system for depropanization, and the balance of the condensed isobutane is passed to a second flash zone of lower pressure where a portion of the isobutane and lighter hydrocarbon including propane is vaporized with resultant chilling of the remaining liquid isobutane. This chilled liquid isobutane is then recycled to the alkylation zone. The second flash drum producing chilled liquid isobutane thereby absorbs part of the refrigeration load, andreduces the. refrigeration require- Patented June 13, 1961 ments of the first flash zone in order to maintain the desired temperature of the alkylation reaction zone;

The present invention relates to an improvement in eiiuent refrigeration of this double liash zone type. As in the foregoing processes using efliuent refrigeration, the liquid hydrocarbon residual efiluent from refrigeration of the alkylation zone contents (said liquid hydrocarbon containing unreacted isobutane and alkylate product) is separated from vaporized hydrocarbons (which are mainly isobutane) and is passed to aqueous washing, then to' fractionation for recovery of the alkylate.

In accordance with this invention vaporized `isobutane from the rst Hash zone is condensed, the resulting con-4 densate is depropanized, at least a portion of the depropanized isobutane condensate is passed to a second flash zone of lower pressure to furnish chilled liquid isobutane for returning to the alkylation reaction zone; concomitantly with this operation the liquid hydrocarbon residual from the effluent refrigeration, which residual has been subjected to aqueous washing, is deisobutanized, the recovered isobutane from this deisobutanizing is passed into indirect heat exchange with the liquid hydrocarbon residual prior to its aqueous washing, and they resulting chilled recovered isobutane is combined for reaction in the alkylation reaction zone with the chilled liquid isobutane from the second flash zone and with olefinic feed stock for the production of alkylate. In this manner the important alkylation conditions of desirable low temperature and high isobutane concentration are readily maintained.

As further features of the present invention, liquid ICC isobutane removed as bottoms from the depropanizing fractionating zone is passed in indirect heat exchange relation with the hydrocarbon feed to said depropanizing fractionating zone; and the said liquid isobutane bottoms may then be further cooled, as by water cooling, beforeV being introduced into the second flash zone. Vaporized-V isobutane removed from the second flash zone is mixed` with the vaporized hydrocarbons removed from the rst flash zone, so that a single compressor-condenser system suflices for the plant.

Advantageously the hydrocarbons from both flash zones are condensed together, suitably `by use of a single compressor and a condenser.

such as ammonia or a Freon in this step. y

In the preferred embodiment of our invention the Wet hydrocarbons from the aqueous washing are rst deisocooling,

ond flash drum is then alkylation zone.

ThisV pre-cooling with spent refrigerant of the hydro-- carbons being fed into the alkylation zone assists in maintaining desired low alkylation temperatures at highthroughput in the reaction vessel. Signicantly also, suchpre-cooling of the recovered isobutane,.which is wet from the aqueous washing,

tion catalyst with water and thereby prolongs its useful-v ness for the alkylation operation. It also eliminates the'. gettlng into the refrigeration system` possibility of Water whereby corrosive situations can develop.

However the use of a cou--v denser sufficiently cooled with a conventional refrigerant can be used exclusively..

and the olefinic feed, which can. be wet from extraneous sourcesserves to dry these-feeds economlcally. Drying suppresses dilution of the alkyla-" The invention is illustrated in the attached drawing wherein the single figure represents a llow diagram of a typical alkylation plant of the pump and time tank type employing the features of the present invention.

Referring to the drawing, the olefin feed stream is introduced by line 10, and any make-up isobutane is added thereto by line 11. It will be understood that the oleiin feed stream is generally a C4 cracking gas fraction containing butanes and butylenes and termed B--B feed, and preferably is one which contains less than about 30` liquid volume percent of normal butane. However, a mixed Ca-C4 olen feed stream can be employed, or other normally gaseous or normally liquid olen feed may be used. The resulting feed stream, mixed with recycled isobutane from line 12, is passed through the feed exchanger 13 which is chilled by ellluent refrigeration as described below. It is then introduced by line 14 into the emulsion recycle line 15 of the pump and time tank alkylation reaction zone system.

This system contains in conventional manner an emulsion recycle pump 16 forcing the emulsion of hydrocarbons in liquid phase and liquid alkylation catalyst through emulsion chiller 17 cooled by eflluent refrigeration as hereinafter described, thence by line 18 to baffled time tank 19, and thence by line 20 containing the usual resistance orifice (not shown) in the portion of that line between time tank 19 and the connection with line 24, back to line 15 for return through the system. A portion of the circulating emulsion is removed from time tank 1 9 by line 22 to settler 23, where the emulsion is allowed to settle into an upper hydrocarbon layer and a lower liquid catalyst layer. The major portion of the settled liquid catalyst layer is recycled by line 24 to the emulsion system, with a minor proportion being withdrawn to recovery by line 25 and fresh make-up catalyst introduced into the system by line 26.

Preferably strong sulfuric acid of about 88-98% strength is used as the catalyst in conventional manner, although other liquid alkylation catalysts which are nonvolatile under the conditions at which isobutane is vaporized in the ilash drums for ellluent refrigeration, such as aluminum chloride-hydrocarbon complex liquid catalyst, can be employed. It will be understood that the liquid acid-hydrocarbon volume ratio in the emulsion recycle system (line 15, pump 16, chiller 17, line 18, time tank 19 and line 20) which constitutes the alkylation reaction zone, is maintained about 1:1, and a contact time in the alkylation zone of about 25-45 minutes is utilized in conventional manner. Where sulfuric acid is utilized as catalyst, makeup 98% H2SO4 is added to keep the system acid at about 88-92% strength. The mol ratio of isobutane to oleiln supplied to the alkylation zone (including isobutane recycle) is substantially in excess of 1:1, and generally is about 4:1 to 10:1. This is accomplished -With the present eflluent refrigeration system by a relatively small fresh feed of make-up isobutane, the major requirement for make-up isobutane being generally furnished as a component of the B-B feed. Also, the present system is capable of maintaining as high as 70 liquid volume percent or more of isobutane in the reactor effluent from the alkylation reaction zone. It will be appreciated that the high molar excess of isobutane in the alkylation zone is primarily maintained by isobutane recycle, and that effluent refrigeration effectively keeps the greater portion of this isobutane recycle in the compressor-condenser system and the alkylation zone, and thus materially reduces the fractionation requirements of the alkylate fractionating system.

'Ihe temperature in the alkylation reaction zone is maintained below about 70 F., and preferably around 50 F., and this is accomplished in accordance with the present invention solely by eluent refrigeration in conjunction with water cooling, and without any other external source of refrigeration. A s shown, the hydrocarbon layer from settler 23 is passed by line 30 to flash drum 31. Here the pressure is dropped from a pressure of about 25-40 lbs. per square inch absolute existing in the alkylation system to approximately atmospheric pressure or below by connecting the suction side of compressor 32 through vapor line 33, compressor trap 34 and vapor line 35 to the upper portion of ilash drum 31. This results in isobutane and lighter hydrocarbons including propane being vaporized in flash drum 31 with resultant chilling of the remaining unvaporized hydrocarbon liquid to about 35 F. or below. A portion of the chilled hydrocarbon liquid is passed by line 36, pump 37 and line 38 to the feed exchanger 13 to pre-chill the feed to the alkylation zone. This portion of the hydrocarbon liquid is then passed by line 39 to the fractionating system for recovery of alkylate as described below.

Another portion of the chilled hydrocarbon liquid from flash drum 31 is passed by line 40 to the emulsion chiller 17 to chill the alkylation reaction zone. In the arrangement shown, it will be understood that the flash drum 31 is preferably arranged at an elevation above the emulsion chiller 17, so that gravity flow is utilized to convey the chilled hydrocarbon liquid through line 40 to chiller or exchanger 17, where a portion of the isobutane and lighter is vaporized to provide refrigeration with an incidental thermosiphon effect, which returns the mixed liquid and vapor through line 41 to the flash drum 31. However, it will be understood that a pump can be provided for positive circulation through the emulsion exchanger 17 if desired.

Vaporized isobutane and propane removed from the flash drum 31 by vapor line 35 pass into compressor trap 34,` where any heavier entrained liquid drops out and can be removed by pump 43 and line 44. The vapors then pass by vapor line 33 to compressor 32 which raises the pressure thereof to about 75-85 lbs. per square inch absolute, and forces them by vapor line 45 through water cooled condenser 46 and line 47 into accumulator 48. From here the liquelled isobutane and propane is removed by line 49 and pump 50 and forced through exchanger 51 and line 52 to depropanizer 53. This fractionating tower is equipped with a re-boiler indicated generally at 54 to maintain a bottom temperature of about 200 F. and is equipped with suflicient trays to effect a rather sharp separation between propane vapor removed overhead by vapor line 55 and liquid isobutane bottoms. The propane vapor is passed through condenser 56 into accumulator 57, from where pump 58 returns a portion thereof through line 59 as retlux to depropanizer tower 513, the balance being discharged by line 6) to storage for LPG or other purposes.

The isobutane bottoms substantially denuded of propane and lighter from tower 53 is passed by line 62 through exchanger 51 to thereby cool the isobutane while heating the hydrocarbon feed to the depropanizer. The partially cooled liquid isobutane then passes by line 63 through water cooler 64 where the temperature is lowered to about F., and then into a second flash drum 65. Here the pressure is dropped again to substantially atmospheric or lower by connecting the suction of compressor 32 through vapor line 33, compressor trap 34, vapor line 35 and branch vapor line 66 to the top of flash drum 65. While the construction shown is satisfactory for a small alkylation unit, it Will be understood that in the case of larger size units, the overhead line 66 from ash drum 65 may desirably be connected through its individual compressor trap to an interstage of a multi-stage compressor unit 32 receiving the gases from ash drum 31 at the compressor suction of the first stage. This results in vaporization of a portion of the isobutane in ilash drum 65 with resultant chilling of the remaining liquid isobutane to about 15-20" F. The isobutane vapors removed from the second flash drum are combined with the vapors from the rst llash drum 31 for passing through the single compressor-condenser System.

The chilled liquid isobutane from ilash drum 65 is passed by pump 68 and line 69 to line 14, where it is mixed with the chilled isobutane-olelin feed to the alkylation Zone after the said feed has passed through exchanger 13. Thus the isobutane recycle from the second flash drum is utilized to further pre-chill the feed to the alkylation zone by mixing therewith, thereby distributing the refrigeration load between the two llash drums.

The hydrocarbon elfluent from line 39, which has been used to chill the feed exchanger 13, passes through the conventional caustic washing and water washing steps indicated generally at 70 and 71 respectively, and thence is introduced by line 72 into deisobutanizer tower 73. This tower is operated to make a sharp separation between isobutane and normal butane and heavier to thereby remove overhead by vapor line 74 an essentially isobutane vapor which passes through condenser 75 into accumulator 76. From here, the condensed isobutane is picked up by pump 77 and a portion returned by line 78 as reux to deisobutanizer tower 73. The remainder is passed by line 79 through water cooler 80 and thence by line 12 to supply -the recycled isobutane which is mixed with the olefin feed in advance of the exchanger 13. Thus, the recycled isobutane from the alkylate fractionating system is pre-chilled in conjunction with the olefin feed in the eflluent exchanger 13, and this mixed stream is then further pre-chilled by mixing with the recycle isobutane from the second ilash drum 65 before the resultant mixture is introduced into the alkylation reaction zone. The chilled hydrocarbon eflluent from ash drum 31 at a temperature of about 35 is capable of lowering the temperature of the feed from around 100 F. to about 50 F.; and the mixing of the substantial proportion of chilled isobutane recycle from flash drum 65 at a temperature of about 15-20 F. further lowers the temperature of the feed to below about 35 F., whereby the emulsion chiller 17 is capable of extracting the remaining heatof reaction in the alkylation zone to maintain the temperature in that zone around 50 F. or below.

The liquid product from deisobutanizer 73' passes by line 82 to product `debutanizer 83, where normal butane is removed overhead by vapor line 84 through condenser 85 to accumulator 86. The liquid normal butane is picked up by pump 87, and la portion thereof is returned by line 88 as rellux, the balance being discharged by line 89 to tankage for feed to an isomerization unit or as blending stock or for other purposes.

The debutanized product passes by line 90 to fractionator 91 where the desired aviation alkylate or high octane motor gasoline alkylate fraction is removed overhead, condensed and discharged to tankage by line 92, with the heavier alkylate bottoms being discharged through cooler 93 and line 94 to tankage to serve'as cracking stock or for other uses.

The following is given as an example of the present invention, and represents the design for an 890 barrel per day aviation alkylate plant. An olefin feed stock is introduced through line at a charge rate of 47.2 bbls./hr. with a composition in mol percent of 3.9% .propane and lighter, 23.2% of isobutane, 48.7% of butylenes, 21.2% of normal butane and 3.0% of C5. Make-up isobutane from line 11 is introduced at the rate of 6.4 bbls./hr. un'th a composition in mol percent of 1.5% propane, 94.5% isobutane and 4.0% normal butane. This is mixed with recycle isobutane from line 12 introduced at the rate of 78.4 bbls./hr. with a composition in mol percent of 0.9% C3, 95.6% isobutane, 0.3% butylenes and 3.2% normal butane. The foregoing mixed feed at a temperature of approximately 100 F. passes through said exchanger 13 and is chilled to 50 F. by hydrocarbon effluent from ash drum 31 having a temperature of 35 F. at the entry to exchanger 13, and a temperature of F. at the exit thereof. The resultant chilled feed is then mixed with chilled recycle isobutane from ash drum 65 supplied at a temperature of 18.5 F. and a feed rate of 122.8 bbls./hr., with a composition in mol percent of 0.04% C3, 85.8% isobutane, 13.2% normal butane, and 0.9% C5 and heavier. Thus more than 60% of the recycle isobutane is from the compressor-condenser system, thereby reducing the volume on the alkylate fractionating system with respect to isobutane recycle to less than 40%, and consequently enabling substantial increase in capacity for a given size alkylation plant.

The total reactor hydrocarbon charge of 254.8 bbls./hr. with a composition in mol percent of 1.1% C3, 76.5% isobutane, 9.5% butylenes, 11.9% normal butane and 1.0% C5 and heavier, is supplied to the alkylation reaction zone at a temperature of about 34 F. 2.6 bbls./hr. of make-up 98% H3SO4 are supplied together with 246.6 bbls./hr. of recycle H3SO5 to the alkylation reaction zone, thereby giving a hydrocarbon to acid volume ratio in the reaction zone of 1:1 with a maintained system acidity of about 92% H3SO4.

Hydrocarbon eluent is removed from settler 23 by line 30 to flash drum 31 'at the rate of 246.6 bbls./hr., having a composition in mol percent of 1.2% C5, 73.0% isobutane, 13.0% normal butane, 0.9% C5 and 11.9% alkylate. In flash drum 31 the pressure is dropped to 16 lbs. per square inch absolute, with resultant flashing of 124.9 bbls./hr. of vapors having a composition in mol percent of 1.8% C3, 84.3% isobutane, 13.0% normal butane and 0.9% C5 and heavier. 121.7 bbls./hr. of chilled hydrocarbon liquid refrigerant is thus provided having a composition in mol percent of 0.4% C3, 60.3% isobutane, 12.9% normal butane, 1.4% C5, and 25.0% alkylate. This chilled hydrocarbon liquid at a temperature of 35 F. passes through feed exchanger 13,

where its temperature is raised to 85 F., and thenceV flows through caustic washing and water washing to the deisobutanizer 73. In order to furnish additional makeup isobutane available at the plant as debutanizer overhead from a polymerization unit, 32.2 bbls./hr. of this debutanizer overhead, having a composition in mol percent of 0.9% C5, 28.5% isobutane, 0.7% butylene, 68.7% normal butane and 1.2% C5, are added by line 96 to deisobutanizer 73, preferably at `a lower level than theY entry of line 72. Here the isobutane recycle previously described is produced as overhead and, after condensation, is returned to the alkylation feed by line 12. The

deisobutanized `bottoms leaves deisobutanizer 73 at theV rate of 75.5 bbls./hr. with a composition in mol percent of 0.1% C3, 2.9% isobutane, 51.4% normal butane, 3.0% C5 and 42.6% alkylate.

The combined vapors from ash drums 31 and 65 (which also include the vapors produced in the refrigeration system of emulsion exchanger 17 which are returned to the ash drum 31), after compression and condensation, provide a charge to depropanizer 53 ata pressure of 8l lbs. per square inch absolute of 168.7 bbls./hr.

having a composition in mol percent of 1.4% C3, 85.8%

isobutane, 12.2% normal butane and 0.6% C5 and heavier.

An overhead from depropanizer 53 is removed at the rate of 2.2 bbls./hr. having a composition in mol percent of 88.4% C3, 9.9% isobutane and 1.7% normal butane. This provides a depropanized bottoms at the rate of 166.5 bbls./hr. having a composition in mol percent of 0.06% C3, 86.9% isobutane, 12.4% normal butane and 0.6% C5 and heavier.

The depropanized bottoms stream is ashed in flash drum 65 at 16 lbs. per square inch absolute, thereby providing a recycle liquid isobutane from the bottom of flash drum 65 at a temperature of 18.5 F. of the quantity and composition set forth above, and this is introduced into the feed to the alkylation zone by line 69. The overhead vapors from the ash drum 65 are removed at the rate of 43.8 bblsJhr. with a composition in mol percent of 0.1% C3, 89.9% isobutane, 9.9% norrnal butane and 0.1% C5, and these vapors are returned to the compressor-condenser system.

The said plant consumes 24.8 bbls./hr. of isobutane, and produces 39.0 bbls./hr. of total alkylate `above C5, from which about 37.1 bbls./hr. of aviation alkylate are obtained.

While the invention has been described in connection with a pump and time tank alkylation unit, it is to be und erstood that it is equally applicable to other conventional types of alkylation reactor systems, such as those employing internal recirculation of the type of so-called Stratco contactors wherein chilling of the emulsion is accomplished by circulating the chilled eluent hydrocarbony liquid through heat exchangers vor tube bundles immersed in the emulsion in the contactor.

Obviously many modifications and variations of the invention as hereinbefore set forth may be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are` indicated inthe appended claims.

We claim:

1. In a process for catalytic isobutane-olefin alkylation employing effluent refrigeration, wherein isobutane in molar excess and olefnic feed stock :are contacted in liquid phase in an alkylation zone with a liquid catalyst under "alkylating conditions, resulting reaction mixture is separated into a liquid hydrocarbon phase and a liquid catalyst phase, separated liquid hydrocarbon phase is passed to a ash zone of lower pressure to evaporate isobutane therefrom and concomitantly chill remaining hydrocarbon liquid, and at least a portion of the chilled hydrocarbon liquid is passed in indirect heat exchange relation with olenic feed stock being introduced into said alkylation zone and is then passed to aqueous washing and to fractionation for the recovery of alkylate therefrom, the improvement which comprises deisobutanizing the said hydrocarbon liquid passed to the said fractionation to recover isobutane liquid therefrom, recycling said recovered isobutane liquid and mixing the same with the said olenic feed stock in advance of the indirect heat exchange with the said chilled hydrocarbon liquid, compressing and condensing vaporized isobutane from said flash zone, depropanizing substantially all of the said condensed isobutane, passing the depropanized isobutane to a second ash zone of lower pressure where a portion of the isobutane is vaporized with resultant chilling of the remaining liquid isobutane, and mixing the said chilled liquid isobutane with said mixed stream of olenic feed stock and recovered isobutane liquid after the said indirect heat exchange of the said mixed stream with the said chilled hydrocarbon liquid and prior to introduction of said mixed stream into said alkylation zone whereby said recovered isobutane liquid and vapor evaporated from the liquid hydrocarbon phase of said reaction mixture are maintained as separate streams.

2. The method according to claim 1 wherein the said,

8 recovered isobutane from the deisobutanizing step is cooled prior to mixing with the said olefinic feed stock.

3. In a process for catalytic isobutane-olefin alkylation wherein isobutane in molar excess and olenic feed stock are contacted in liquid phase in an alkylation reaction zone with a liquid catalyst under alkylating conditions, resulting reaction mixture is separated into a liquid hydrocarbon phase and a liquid catalyst phase, separated liquid hydrocarbon phase is passed to a first ash Zone of lower pressure to evaporate isobutane therefrom and concomitantly to chill remaining hydrocarbon liquid, at least a portion of said chilled hydrocarbon liquid is passed in indirect heat exchange relation with the contents of said alkylation reaction zone for providing effluent refrigeration thereof, and cold liquid hydrocarbon residual froml refrigerating is disengaged from associated hydrocarbon vapors, then passed to aqueous washing and to fractionation for the recovery of alkylate therefrom, the improvement which comprises: deisobutanizing said liquid hydrocarbon residual passed to said fractionation after said aqueous washing to recover isobutane liquid therefrom, passing the resulting recovered isobutane liquid into indirect heat exchange with said liquid hydrocarbon residual before said aqueous washing, thereby cooling said recovered isobutane liquid, condensing vaporized isobutane from said first ash Zone, depropanizing resulting isobutane condensate, passing at least a portion of the depropanized isobutane condensate to a second ash zone of lower pressure where a portion thereof is vaporized with resultant chilling of the remaining liquid isobutane, and combining for reaction in said alkylation reaction zone said chilled remaining liquid isobutane and with olenic feed stock and with the cooled recovered isobutane liquid whereby said recovered isobutane liquid and vapor evaporated from the liquid hydrocarbon phase of said reaction mixture are maintained as separate streams.

4. The method according to claim 3 wherein said recovered isobutane is mixed with the olenic feed stock in advance of the indirect heat exchange with said liquid hydrocarbon residual, and the chilled remaining liquid isobutane from the second flash zone is combined for reaction in said alkylation reaction Zone with the mixed stream of oleiinic feed stock and recovered isobutane after said indirect heat exchange.

5. The method according to claim 4 wherein vapors from said second flash zone are combined with the vaporized isobutane from said first flash zone for condensation therewith.

6. The method according to claim 4 wherein the depropanized, condensed isobutane is cooled prior to flashing in said second llash zone.

Jenny et al. Oct. 21, 1947 Putney Dec. 29, 1953 

1. IN A PROCESS FOR CATALYTIC ISOBUTANE-OLEFIN ALKYLATION EMPLOYING EFFLUENT REFRIGERATION, WHEREIN ISOBUTANE IN MOLAR EXCESS AND OLEFINIC FEED STOCK ARE CONTACTED IN LIQUID PHASE IN AN ALKYLATION ZONE WITH A LIQUID CATALYST UNDER ALKYLATING CONDITIONS, RESULTING REACTION MIXTURE IS SEPARATED INTO A LIQUID HYDROCARBON PHASE AND A LIQUID CATALYST PHASE, SEPARATED LIQUID HYDROCARBON PHASE IS PASSED TO A FLASH ZONE OF LOWER PRESSURE TO EVAPORATE ISOBUTANE THEREFROM AND CONCOMITANTLY CHILL REMAINING HYDROCARBON LIQUID, AND AT LEAST A PORTION OF THE CHILLED HYDROCARBON LIQUID IS PASSED IN INDIRECT HEAT EXCHANGE RELATION WITH OLEFINIC FEED STOCK BEING INTRODUCED INTO SAID ALKYLATION ZONE AND IS THEN PASSED TO AQUEOUS WASHING AND TO FRACTIONATION FOR THE RECOVERY OF ALKYLATE THEREFROM, THE IMPROVEMENT WHICH COMPRISES DEISOBUTANIZING THE SAID HYDROCARBON LIQUID PASSED TO THE SAID FRACTIONATION TO RECOVER ISOBUTANE LIQUID THEREFROM, RECYCLING SAID RECOVERED ISOBUTANE LIQUID AND MIXING THE SAME WITH THE SAID OLEFINIC FEED STOCK IN ADVANCE OF 